We propose to investigate the genetic relationship between the various populations of the common House Mosquito present in the Boston area. By comparing the electrophoretic mobility of selected isozymes, we shall determine (1) whether the autogenous, anautogenous and rural forms may be characterized, (2) whether the populations are genetically isolated, (3) if so, whether isolation is absolute, and (4) whether one population may possess more genetic variability than others. In addition, we will observe how these populations may be affected by inbreeding. We shall study the blood-feeding habits of each population and determine whether man-biting may be associated with certain populations or combinations of populations. Ultimately we hope to devise procedures for replacing man-biting Culex pipiens by others that do not frequently feed on man.